When a certain compound has two or more crystal states, these different crystalline states are called crystal polymorphism. It is generally known that, when crystal polymorphism exists, the transition of crystal form may occur and, further, the crystal polymorphs (crystal forms) in crystal polymorphism are different from each other in stability and physical properties.
The transition of crystal form in the crystal polymorphism is a phenomenon that is frequently found, for example, in drying, grinding, and storage in chemical industry. The transition of the crystal form sometimes leads to serious problems such as consolidation, extension of crystal, powdering, and heat generation. In particular, in the field of agricultural chemicals, the transition of crystal form after formulation sometimes has a significant effect on the properties and quality of agricultural chemicals, for example, efficacy of agricultural chemicals and storage stability of formulations. Highly stable crystal forms have been developed in order to avoid such problems.
For example, patent document 1 describes crystal polymorphism of methazachlor which is an active ingredient for weeding. Specifically, an aqueous suspension composition comprising a crystal polymorph (1A) obtained by crystallization from cyclohexne or toluene causes agglomeration, and, consequently, the composition becomes heterogeneous and not sprayable. On the other hand, an aqueous suspension composition comprising crystal polymorph (1B) obtained by crystallization in the presence of an organic solvent that is miscible with water, polar, and inert does not cause agglomeration and can maintain good properties.
In patent document 2, problems such as consolidation and heat generation caused by the solid-phase transition of polymorphic crystal of Quizalofop-P-ethyl are avoided by obtaining stabilized crystals. Further, in patent documents 3 and 4, the efficacy of thifluzamide which is a fungicidal active ingredient is improved through an improvement in elution of thifluzamide into water by the transition of crystal form of the thifluzamide.
2-Ethyl-3,7-dimethyl-6-(4-(trifluoromethoxy)phenoxy)-quinoline-4-yl methyl carbonate (hereinafter sometimes referred to simply as “compound I”) is a compound having a high insecticidal activity (patent documents 5 and 6). Compound I exerts a high insecticidal activity particularly against Lepidoptera, Hemiptera, Coleoptera, Acari, Hymenoptera, Orthoptera, Diptera, and Order Thysanoptera and is expected to be useful as an active ingredient for agricultural and horticultural insecticides. Up to now, any crystal of compound I having high physicochemical stability has not been reported.